BU-501a: Discharge Characteristics of Li-ion

Learn about the difference of energy and power requirements in a battery.

The early Li-ion battery was considered fragile and unsuitable for high loads. This has changed, and today lithium-based systems stand shoulder to shoulder with the robust nickel and lead chemistries. Two basic types of Li-ion have emerged: The Energy Cell and the Power Cell.

Energy Cell

The Li-ion Energy Cell is made for maximum capacity to provide long runtimes. The Panasonic NCR18650B Energy Cell (Figure 1) has high capacity but is less enduring when discharged at 2C. At the discharge cutoff of 3.0V/cell, the 2C discharge produces only about 2.3Ah rather than the specified 3.2Ah. This cell is ideal for portable computing and similar light duties.

Figure 1: Discharge characteristics of NCR18650B Energy Cell by Panasonic.
The 3,200mAh Energy Cell is discharged at 0.2C, 0.5C, 1C and 2C. The circle at the 3.0V/cell line marks the end-of-discharge point at 2C.

Power Cell

The Panasonic UR18650RX Power Cell (Figure 2) has a low capacity but excellent load capabilities. A 10A (5C) discharge has minimal capacity loss at the 3.0V cutoff voltage. This cell works well for applications requiring heavy load current, such as power tools.

Figure 2: Discharge characteristics of UR18650RX Power Cell by Panasonic.
The 1950mAh Power Cell is discharged at 0.2C, 0.5C, 1C and 2C and 10A. All reach the 3.0V/cell cut-off line at about 2000mAh. The Power Cell has moderate capacity but delivers high current.

The Power Cell permits a continuous discharge of 10C. This means that an 18650 cell rated at 2,000mAh can provide a continuous load of 20A (30A with Li-phosphate). The superior performance is achieved in part by lowering the internal resistance and by optimizing the surface area of active cell materials. Low resistance enables high current flow with minimal temperature rise. Running at the maximum permissible discharge current, the Li-ion Power Cell heats to about 50ºC (122ºF); the temperature is limited to 60ºC (140ºF).

To meet the loading requirements, the pack designer can either use a Power Cell to meet the discharge C-rate requirement or go for the Energy Cell and oversize the pack. The Energy Cell holds about 50 percent more capacity than the Power Cell, but the loading must be reduced. This can be done by oversizing the pack, a method the Tesla EVs use. The battery achieves exceptional runtime but it gets expensive and heavy.

Discharge Signature

One of the unique qualities of nickel- and lithium-based batteries is the ability to deliver continuous high power until the battery is exhausted; a fast electrochemical recovery makes it possible. Lead acid is slower and this can be compared to a drying felt pen that works for short markings on paper and then needs rest to replenish the ink. While the recovery is relatively fast on discharge, and this can be seen when cranking the engine, the slow chemical reaction becomes obvious when charging. This only gets worse with age.

A battery may discharge at a steady load of, say, 0.2C as in a flashlight, but many applications demand momentary loads at double and triple the battery’s C-rating. GSM (Global System for Mobile Communications) for a mobile phone is such an example (Figure 3). GSM loads the battery with up to 2A at a pulse rate of 577 micro-seconds (μs). This places a large demand on a small battery; however, with a high frequency, the battery begins to behave more like a large capacitor and the battery characteristics change.

Figure 3: GSM discharge pulses of a cellular phone.The 577 microsecond pulses drawn from the battery adjust to field strength and can reach 2 amperes.

Courtesy of Cadex

In terms of longevity, a battery prefers moderate current at a constant discharge rather than a pulsed or momentary high load. Figure 4 demonstrates the decreasing capacity of a NiMH battery at different load conditions from a gentle 0.2C DC discharge, an analog discharge to a pulsed discharge. Most batteries follow a similar pattern in terms of load conditions, including Li-ion.

Figure 4: Cycle life of NiMH under different load conditions.
NiMH performs best with DC and analog loads; digital loads lower the cycle life. Li-ion behaves similarly.

Source: Zhang (1998)

Figure 5 examines the number of full cycles a Li-ion Energy Cell can endure when discharged at different C-rates. At a 2C discharge, the battery exhibits far higher stress than at 1C, limiting the cycle count to about 450 before the capacity drops to half the level.

Figure 5: Cycle life of Li-ion Energy Cell at varying discharge levels.
The wear and tear of all batteries increases with higher loads. Power Cells are more robust than Energy Cells.

Source: Choi et al (2002)

Simple Guidelines for Discharging Batteries

Heat increases battery performance but shortens life by a factor of two for every 10°C increase above 25–30°C (18°F above 77–86°F). Always keep the battery cool.

On high load and repetitive full discharges, reduce stress by using a larger battery.

A moderate DC discharge is better for a battery than pulse and heavy momentary loads.

A battery exhibits capacitor-like characteristics when discharging at high frequency. This allows higher peak currents than is possible with a DC load.

Nickel- and lithium-based batteries have a fast chemical reaction; lead acid is sluggish and requires a few seconds to recover between heavy loads.

All batteries suffer stress when stretched to maximum permissible tolerances.

Last updated 2016-05-18

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Batteries in a Portable World

Comments

On May 7, 2011 at 9:03pm

HITESH PATEL wrote:

battery full lod discharging chart

On May 25, 2011 at 12:17pm

Samuel Maher Youssef wrote:

please i want to install solar system,and i will use flood deep cycle battery,
i will use four battery 12 volt DC, can i use two battery each other 24 volt and what advantage to use 4 battery.
thanks a lot.

On June 6, 2011 at 10:06pm

Susanta Kumar Sahu wrote:

Dear Sir/Madam,
I am Susanta Kumar Sahu to inform you that i have no knowledge about battery discharge (EX: 180AH battery, connecting with load that depends on customer how much it give back up like this ).Can you tell BACK UP concept of all bettery?

Thank You.
Susanta Kumar Sahu

On June 9, 2011 at 11:42pm

Gaurav wrote:

Is there any empirical formula to calculate battery DEPTH of Discharge for a given lifetime?

2) Is there any equation where we can determine the remaining time in a battery upon
knowing the discharge voltage during operation?

3) What exactly do you mean by efficiency of the battery ?

4) What is the effect of soldering on a Li-ion cell for paralleling by our self ?

On November 17, 2011 at 9:26pm

gary pione wrote:

can anyone answer question number one from pier ? can peukerts equation be used for lithium type batteries?

On November 17, 2011 at 9:33pm

Ian wrote:

You may have missed this, gary: “The Peukert Law of a battery is exponentialand the readings for lead acid are between 1.3 and 1.4. Nickel-based batteries have low numbers and lithium-ion is even better.” Missing space in there. Different chemistries have different values.

Soldering directly onto a Li-ion cell is not recommended. They can explode.

On November 17, 2011 at 9:55pm

gary pione wrote:

thanks ian. i saw that on the second read thru. i have never been a good student

On November 25, 2011 at 9:53am

TAHIR HUSSAIN wrote:

Dear Sir,
I live in Pakistan and i am working in lead acid battery company.
My question is, How can i calculate Peukert’s number by theoretical or practical and each battery (size wise) has a different peukert number.

Regards,
TAHIR

On January 8, 2012 at 9:17pm

Terence Cheong wrote:

Please infrom me how to calculate the time for discharging a traction battery with 560Ah & 420

On February 8, 2012 at 4:30am

Komal wrote:

how to calculate the charging and discharging time of Li-ion battery with specification of 100 Ah, 12 V.and applying 2 A constant current.?????

On February 23, 2012 at 4:41am

Sheldon Patnett wrote:

Yes Peukert’s Equation can be used for Lithium batteries. Their exponents are closer to 1.0 than lead acid Batteries.

On February 23, 2012 at 9:42pm

Pier wrote:

How exactly do you define one cycle in a Li-Ion cell ? I find cycle count in Lenovo thinkpads but not sure as to how they compute it !!!

On May 8, 2012 at 6:13am

Syed wrote:

Hello,
How to calculate the charging and dischargin time of a Li- ion polymer battery of capacity 1230mAh, 3.7V applying 250mA constant current?
Thank You

On May 8, 2012 at 6:19am

Syed wrote:

Hello,
How do we calculate the no. of hours a battery can provide on continuous discharge of 250mA of capacity 1320mAh?
Also providing the voltage the battery can provide after every hour of discharge of 250mA would be good.
Note:
Nominal voltage of the battery is 3.7V.
max operating range is 2.75V to 4.2V.
max continuous discharge current is 1000mA
internal resistance is 150milli ohm
Thanks

On July 24, 2012 at 1:20am

Muhammad Ahmed wrote:

My Dear friends;
I designed a solar system in which appliance load is 500 Watt and appliance watt per day is 1500.
So I used 150watt 2 solar panel, 24volt and 12 A Solar charge controller, 2 batteries of 125Ah each.
Normally 7 hours sunlight.

My problem is that I want to calculate in how much time period batteries will again recharge.

Please help me in this problem

Thanks

On August 30, 2012 at 10:28am

Johnny wrote:

my cell battry is bulging , it’s a li-ion, and i was wondering how i make it safe(er) to dispose of, can you help with that? the phone says “use authentic battery” so i’m afraid it might explode,

but by actual run i got 5-7 hour only. i’m i using wrong battery or my calculation wrong..

On October 18, 2012 at 9:45pm

Ian wrote:

7Ah is the capacity at a rate that flattens the battery in 20 hours. Your load is much higher than that so you need to take the Peukert effect into consideration. SLA batteries have quite high Peukert effect. The Peukert calculation is much more complicated than what you have done, but you could use the top graph instead to make it easier.

On February 11, 2013 at 3:48am

Suresh Patil wrote:

If inverter efficiency is around 80%, current from 12 volts for 19W load is approx. 2 amps.
When 3 batteries are in parallel, You have a 7.2 x 3 i.e.21.6AH (@ 20 Hr. rate.)
Using Peukert equation calculation, you should get 8Hr. 30Min. approx. This makes the battery fully discharged. For better life, batteries are not discharged beyond 80%. So inverters’ cut off volts are adjusted to higher value. Probably, the inverter efficiency may be even less than 80%. If you find exact current from the batteries, Peukert formula will give you quite accurate duration. There is no much complication.

On February 23, 2013 at 10:25pm

ashish wrote:

If possible, kindly share the info on making an
SMPS charger of 4000 Watts and above

but by actual run i got 5-7 hour only. i’m i using wrong battery or my calculation wrong..———————————————————————————
The Peukert effect. Your 7ah battery is too small. The rate in the above chart for 120Ah compared to you 7Ah*3=21Ah battery. Lead acid is 1.3 to 1.4. Your is 19w /12v = 1.58 Amp draw. 120/21 for battery in above chart *1.58 = proportional equivalent~ 9.0 amp so look the 9 amp and it gives capacity reduction of about 50% in the Peukert chart so you will get 20 hours run time down to 10 hours just from that, and even worst as your batteries age. SLA rating is only good for long slow discharge 20AH is 1 Amp for 20 Hours. Take 10x times (10Amps) that out in 2 Hours you get only roughly half to 1/3 that amount if your lucky. That is why my project ebike will have NiMH battery instead of SLA. The higher cost 5x is justified in lifetime use and performance. LiPo4 is still too much expense and funny picky charging/discharge/ quality.

On March 6, 2013 at 12:50pm

Slocket wrote:

Sorry correction, your example only 13 hours use * 50% = 6.5 hours as you discovered, I was using 20 hour run for 10 hours use.

SLA rating is only for low current draw. Peukert charts are very much relevant. NiMH is twice that of SLA in rating for real world application using any kind of Medium to Heavy use draw. Medium use is >10% current rating of battery capacity. Low is less than 1<%.

Your example of three 7aH batery for 21 Ah array pulling anything more than 2-3 Amps is going to cut your real amp hour capacity to 50% for SLA. You really need to buy 10x more battery or get NiMH—though NiMH self discharge over time quickly over several days in a solar array.

On October 31, 2013 at 12:33pm

LALIT wrote:

SIR PLEASE TELL ME HOW THE HRD END CRURRENT CALCULATE

On November 15, 2013 at 12:38am

vishal wrote:

Dear sir
I have One 3.7V,600mAh Li-ion battery that battery have DoD is 27% but i want to DoD 70% above that. So what is Procedure for this any circuit have built or other..Please Suggest me.
Give me process for improve battery DoD.

On January 12, 2014 at 11:44am

Anand patel wrote:

i want to know about the normal c20 and c10 rated battery and how to calculate, how much kWh(unit) can be obtained form particular battery like C10 26Ah dc12V battery how much kWh can be obtained at 12V and for C20 Rating Battery.

On March 26, 2014 at 3:01am

okugbesan ibrahim wrote:

how can i calculate 50%volt shutdown on a 24vdc/1400amps inverter batterry.
NB: Inverter capacity is 30kva

On April 2, 2014 at 3:55am

Dj wrote:

i Have 24 numbers of battery, each having 2V,600Ah connected in series with only 400 Watt load that means 48V of my system So can you help me how to calculate the back up time of this system.

On May 31, 2014 at 1:46pm

Bob Sandor wrote:

What is the correct formula to determine how many hours I can draw .028 amps from a 12 volt 700 amp hour lead acid battery before the battery voltage drops to 11 volts?

On June 26, 2014 at 10:13am

Thomas Soares wrote:

A lead acid battery can be transformed to a non acid one. Remove the acid, clean several times with distiled hater and then fill with a solution of KAl(SO4)2 Potassium Alum. This kind of conversion will result in a new kind of energy source: 1) Less voltage; 2) Allows 100% discharge (even shot circuit) with no damage; 3) Fast recharge, but with pulsed DC; 4)Non toxic.

On August 17, 2014 at 5:33am

Solid gold wrote:

A battery of 12v 40ah and 12v 80 ah in parallel , which battery would discharge first?

I need to know what is the actual battery run time during the failure of main source? does the calculation load shall take on the total load of equipment or the ups rating 10kVA?

Kindly please advise how to calculate and what is the best formula to used.

On February 3, 2015 at 7:56am

TITTY VARGHESE wrote:

hi, I need some clarification of UPS battery run time calculation. The detail as follow:
UPS Size : 10kVA
Battery Voltage : 12V
Battery Ah Rating: 100
Battery Qty: 32
Inverter Eff.: 93.5%
I need to know what is the actual battery run time during the failure of main source? does the calculation load shall take on the total load of equipment or the ups rating 10kVA?
Kindly please advise how to calculate and what is the best formula to used.

On February 28, 2015 at 10:07am

Olga Palizo wrote:

How do I calculate to get the total lead in battery? I am doing the TIER II report. MSDS indicates 60% but how do I get the lbs? The battery is used on stand up riders Model # 118-D125-15 weight of battery is 2485

On April 3, 2015 at 1:05am

NC Malviya wrote:

Sir, I like to know, Inverter of 850 KVA with load 700W (app) installed with 150 Ah battery. If battery is fully charged, how much time it will last in normal time.

On April 17, 2015 at 10:14pm

Thomas wrote:

Dear Sir,
I want to size the battery and its charger for a prime rated generator. I had tried it but not sure whether this correct or not. Kindly advice:

HENCE , 3 BATTERIES ARE NEEDED FOR A 700 WATT LOAD ON A 3 BATTERY SYSTEM (36 VDC) for 3 hrs backup.

Mail me at : amit@elnova.com
www.elnova.com

On August 31, 2015 at 4:52am

Ranbir wrote:

How i an find out electromotive force series if zinc -0.76 v and lead -0.13 v. what would the emf of a cell be if the electrodes were lead and zinc

On September 6, 2015 at 1:50am

yadav wrote:

How much time can glows a 170volts bulb with the 240volts of li-ion battery

On April 17, 2016 at 8:56am

IqbalHamid wrote:

I am using TWO batteries attached to my laptop at the same time. I have noticed that Windows fuslly discharges the first battery before swtiching to the second battery. This is supposed to be bad according to this page as it can cause cell reversall and overdischarging. Do circuits in modern laptop batteries prevent this?

Does anyone know of any software or utility which will allow me to set the point (discharge level) at which Windows will switch to using the second battery? Thanks.